The present invention relates to improvements in controlled deflection rolls such as are used in the papermaking industry and more particularly to improved arrangements wherein roll shells are loaded toward the nip and are stabilized on a supporting through shaft.
More particularly, this invention relates to controlled deflection press rolls which have been called self-loading rolls. In this type of controlled deflection roll, a rotatable roll shell is carried on a stationary through shaft and force means loads the roll shell in the direction of the nip supporting it on the shaft. This force means not only controls the nip pressure but controls the uniformity or nonuniformity desired along the length of the nip by controlling the forces at different axial locations along the length of the roll shell.
Such self-loading controlled deflection rolls have conventionally used sliding hydraulically supported shoes supported on the shaft and applying an inner force to the roll shell or have transmitted a force from the shaft to the roll shell by a hydraulic pool of oil which is contained by seals.
One of the controlled operational functions of the roll involves requirements at start-up and shut-down wherein the nip must be loaded or unloaded Various ways have been devised to accomplish this and a conventional way is to merely unload the loading means which forces the roll shell toward the nip and other means employed have used positive loading and unloading means by shoes or pistons applying a force to the inside of the roll shell in a direction opposite of the nip. A requirement of a self-loading roll is that it be capable of uniform stable operation at the high speeds encountered in present paper machines. Because of the high forces involved and the large weights, vibrations can occur which if not avoided, will cause chattering and barring on the paper web and result in defects of the finished paper. Another problem encountered is axial roll oscillation which if allowed to occur, can cause damage and nonuniformity in the pressed paper web and also cause damage to the felts so that if this factor is controlled, felt life will improve. Defects in operation such as vibration and oscillation will also cause damage to the outer surface of the roll shell requiring more frequent grinding and resurfacing than otherwise would be necessary.
It is accordingly an object of the present invention to provide an improved self-loading roll construction which avoids disadvantages heretofore present in the prior art and which provides improved loading and unloading functions for the roll. A further object of the invention is to provide an improved self-loading roll structure which avoids or eliminates vibration by damping and one which eliminates the need for ball bearings wherein the shell rotates only on an oil film.
A further object of the invention is to provide an improved self-loading roll structure which eliminates axial roll oscillation and thereby improving felt life and lengthening the time between grinding in applications such as in paper machine calenders.
A still further object of the invention is to provide an improved self-loading roll structure where manufacturing accuracy can be increased in that supporting bearing pads and main pistons for applying load operate on the same shell bore. A further overall object of the invention is to provide an improved self-loading roll structure which eliminates the need for more expensive bearings and other parts, excludes the need for external arms and pistons and eliminates the need for oil feed to bearings in the main pistons and reduces the overall cost of construction and assembly.